In natural gas engines, a pre-chamber is commonly associated with each cylinder. An electronic controlled fuel admission valve is used to provide fuel to the pre-chamber to facilitate the ignition of the mixture in the pre-chamber. When a solenoid in the pre-chamber fuel admission valve is energized, pressure is increased against the action of a spring force, and a pre-chamber fuel admission valve is opened. When the solenoid is de-energized, the combined forces of the spring and the force exerted by the mixture in the pre-chamber exceed the force exerted on the side remote of the pre-chamber, and the pre-chamber fuel admission valve is closed. Due to the high temperature and vibration that a pre-chamber fuel admission valve is exposed to, the pre-chamber fuel admission valve can degrade and lose certain functions after a short time of operation. Combustion residues and particulate matters in the fuel supply lines can also increase the wear of the pre-chamber fuel admission valve, which may cause the valves to leak, and consequently the cylinder to misfire.
Such leakage is a common problem for pre-chamber fuel admission valves. The leakage of pre-chamber fuel admission valves may result in a rough running of the engine and an increase in the consumption of combustion fuel. The leakage of the pre-chamber fuel valve can dramatically change the Air Fuel Ratio (AFR) in the pre-chamber, due to the smaller volume of the pre-chamber as compared to the main chamber. The AFR is precisely controlled in the pre-chamber to ensure the ignition, so when the AFR deviates from the desired value due to the pre-chamber fuel admission valve leakage, the engine may not start properly, or cause a deviation of AFR from an optimum firing range leading to a misfire in the engine. Since the engine may have a larger number of cylinders and pre-chamber fuel admission valves, and many factors can affect engine performance, it can be very time-consuming and costly to debug gas engine misfire issues in the field to find the root cause. To determine which cylinders or valves are working properly, it may not be practical or cost effective to directly measure the pre-chamber fuel admission valve movement since the tip of pre-chamber fuel admission valve is located within the pre-chamber, or by directly measuring the temperature in both pre-chamber or main chamber, as the combustion temperature can reach over 2000° C.
One example of a system and method for detecting an engine cylinder misfire is disclosed in U.S. Pat. No. 6,243,641 (“the '641 patent”) to Andrews et al. The disclosed system and method includes a single gauge-type pressure sensor positioned in the exhaust manifold to detect misfires in all cylinders of an internal combustion engine. The pressure sensor detects the exhaust manifold pressure and feeds a signal to a microcomputer via an analog-to-digital converter. A data processing device monitors the pressure waveform created by the data from the sensor to determine if a full or partial misfire occurs. If a cylinder suffers from a partial or complete misfire, the strength of the pressure pulse for that cylinder will be reduced, thus, allowing the data processing device to identify the misfire. The data processing device may determine a misfire by computing an average peak pressure for each combustion cycle, a pressure threshold as a function of engine speed and fuel consumption rate, and a minimum pressure value based on the difference between the average peak pressure and the pressure threshold. The data processing device may alternatively determine a misfire by first computing a coefficient of variation between an observed pressure pulse and the average peak pressure and then comparing the coefficient of variation with a pressure threshold to determine if at least a partial misfire has occurred. However, pulsating exhaust flows from each cylinder may interfere with each other due to the overlap of exhaust valve phase. The interference of exhaust flows may limit the effectiveness of the method disclosed in the '641 patent when the method is applied to engines with large cylinders.
Accordingly, there is a need for improved pre-chamber fuel admission valve diagnostics. Various aspects of the disclosure may solve one or more of these problems and/or disadvantages.